1. Field of the Invention
This invention relates to a device for displaying a physical measure such as, for example, the running distance of an automobile measured utilizing a reference signal generated at predetermined intervals.
2. Description of the Related Arts
Due to the mounting trend toward international trade, devices such as automobile odometers have been developing which can display the running distance of the automobile in both kilometers and miles.
As one way for converting units of kilometers to miles and vice versa, it has been considered to perform the conversion of units by storing the running distance in a predetermined memory in units of kilometer for example, and then convert it utilizing the approximation equation 1 mile =1.609344 km.
However, not only because the number of digit in the processing is large, but also because the operation is a binary one while the display is decimal, so many different kinds of conversions are necessary. The operation requires large size processing circuits, microcomputers, etc., and makes the device complicated.
In this kind of system, the actual running distance is formed in kilometer units from the prestored number of pulses generated in synchronization with the rotation of the wheel (reference pulses) per kilometer and the actually counted number of pulses of this, is utilized and the number of pulses per mile is stored in a memory in addition to the number per kilometer, it would be possible to display the distance in units of miles as well.
However, even if the output period of pulses is set so that the number of pulses per kilometer is an integer, the number of the pulses per mile will not be an integer too.
That is, if the output period of the pulses is set so exactly 637 pulses are output per kilometer, since 1 mile =1.609344 kilometer, approximately 1025.152128 pulses will be generated per mile.
By adding one mile each time 1025 pulses are counted as an approximation, it is possible to fairly accurately display the cumulative distance of automobile running in miles with an extremely small counting capacity.
However, with this method, the error is rather small while the cumulative running distance is relatively small, but when the cumulative running distance becomes large, a problem arises in that the error from the actual running distance increases.